Research progress on the correlation between lncRNA and the pathogenesis of COPFD

HE Chan-yi, DING Yi-peng

1.Department of General Medicine, Hainan Provincial People's Hospital Hainan Hospital Affiliated to Hainan Medical University, Haikou 570100, China

Keywords:LncRNA Chronic obstructive pulmonary diseases Biomarkers

ABSTRACT Chronic obstructive pulmonary disease is a common chronic disease with high morbidity and mortality. Early prevention, diagnosis and treatment of chronic obstructive pulmonary disease can effectively reduce its morbidity, improve prognosis, and reduce the economic burden of patients' families. With the deepening of molecular biology research, lncRNAs have become a research hotspot in recent years. They are involved in the occurrence, development and prognosis of diseases, providing new directions for disease research. This article reviews the research progress on the biological characteristics of lncRNAs and their association with the causes, pathological changes and therapeutic drugs of chronic obstructive pulmonary disease.

1. Introduction

Chronic Obstructive Pulmonary Diseases (COPD) is a preventable and treatable chronic disease characterized by persistent airflow limitation. It is one of the diseases with high morbidity and mortality in the world. Early prevention, early diagnosis and early treatment of diseases can effectively reduce its occurrence and development.Long noncoding RNAs (lncRNAs) are a class of noncoding RNAs with transcripts which longer than 200 nucleotides. In recent years,with the in-depth study of molecular biology, it has been found that lncRNAs play important functions in regulating cell proliferation,apoptosis, invasion and angiogenesis, and are closely related to diseases. Its findings provide a new entry point for the study of certain diseases. This article mainly reviews the research progress of the relationship between lncRNA and chronic obstructive pulmonary disease.

2. Biological properties of lncRNAs

LncRNAs are transcripts longer than 200 nucleotides and have functions including cis- or trans-transcriptional regulation,organization of nuclear domains, and regulation of protein or RNA molecules [1]. Previously, most scholars believed that the encoded polypeptides were non-functional, but recent studies have shown that some lncRNAs can actually encode small peptides and participate in regulation [2].

2.1 Discovery of lncRNAs

As early as 1990, classical lncRNAs such as the H19 imprinted gene have been discovered. However, it was initially considered to be the "noise" of genome transcription, a by-product of RNA polymerase Ⅱ (Pol Ⅱ) transcription, and had no biological function. One year later, Brown et al. found that lncRNA Xist can silence one of the two X chromosomes in females, so that the amount of protein encoded in female organisms tends to be consistent with male organisms [3]. Although thought to be a special case at the time, the discovery caught the attention of many researchers. With the in-depth study of the molecular mechanism of lncRNA, more and more studies have found that lncRNA plays an indispensable role in the activities of many life and diseases.The discovery of HOX Antisense Intergenic RNA (HOTAIR) in 2007 suggested that lncRNAs may have remote regulation. Its discoverers, Rinn et al., published an article in Cell that lncRNA HOTAIR can interact with PRC2, mediate H3K27me3 modification,and silence gene expression at the site of action [4]. Since then,lncRNAs have become a research hotspot in the past decade.

2.2 Biosynthesis of lncRNAs

Most lncRNAs are transcribed by RNA polymerase Ⅱ (Pol Ⅱ)and have five-prime cap(m7GpppN)and a poly-A tail at the 3' end,which are considered to be similar in transcription and processing to mRNA. Unlike mRNA, some lncRNAs transcribed by Pol Ⅱ are processed inefficiently and remain in the nucleus, while others are spliced and exported into the cytoplasm[5].

2.2.1 Nuclear retention of lncRNAs

Some lncRNAs are transcribed by deregulated Pol Ⅱ, retained on chromatin, and subsequently degraded by nuclear exosomes.Most lncRNAs have certain U1 small nuclear RNA (U1snRNA)binding motifs that can recruit U1 small nuclear ribonucleoprotein(U1snRNP) and associate with Pol Ⅱ at different sites through it.In many lncRNAs, the sequence between the 3' splice site and the branch point is longer and contains a shorter polypyrimidine tract(PPT), resulting in inefficient splicing.The nuclear localization of lncRNAs is coordinated by cis-sequence motifs and trans-factors. A nuclear retention element (NRE)U1snRNA-binding site and C-rich motif can recruit U1snRNP and heterogeneous nuclear ribonucleoprotein K (hnRNPK), respectively,to enhance nuclear localization of lncRNAs. Other differentially expressed RNA binding proteins (RBPs), such as peptidyl proline isomerase E (PPIE) 6, inhibit the splicing of the lncRNA group,resulting in their nuclear retention [6].

2.2.2 Output of lncRNAA large number of lncRNAs are exported into the cytoplasm. Longchain and a/u-rich transcripts, which contain one or only a few exons, depend on the nuclear RNA export factor 1 (NXF1) pathway for export [6]. After reaching the cytoplasm, lncRNAs may undergo a specific sorting process, assigning different lncRNAs to specific organelles or distributing in the cytoplasm, and associate with different RNA-binding proteins (RBPs).

Half of 70% of the cytoplasmic lncRNAs are present in the multimeric fraction. Certain cis-elements contribute to the localization of lncRNAs on the ribosome, such as the long "pseudo"5" untranslated regions, because they precede the "pseudo open reading frames" in the lncRNAs. The degradation of ribosomeassociated lncRNAs may be caused by a triggered by a translationdependent mechanism.

Some lncRNAs are segregated to mitochondria by unknown mechanisms. For example, the RNA component of the mitochondrial RNA processing endoribonuclease (RMRP) is recruited to mitochondria. Once RMRP reaches the mitochondria, it is bound and stabilized by G-richRNA sequence-binding factor 1 (GRSF1),allowing it to accumulate in the mitochondrial matrix.

RNA sequencing of human blood exosomes revealed that a large number of lncRNAs were contained in them. It is unclear how lncRNAs are segregated into exosomes, but the mechanism may involve the binding of RBPs to specific sequence motifs[5].

2.3 Physicochemical properties and biological functions of lncRNAs

LncRNAs have spatiotemporal and tissue specificity [7], regulatory diversity [8], and relatively conserved sequence structures[9].

The distribution of lncRNAs in the nucleus, cytoplasm and organelles of different tissues and cells varies. In different developmental stages of the same tissue or organ, its expression level may be different.

LncRNAs can participate in the regulation of gene expression at multiple levels, including regulation of RNA transcription and localization in eukaryotic cells, epigenetic regulation, and posttranscriptional regulation of RNA processing, translation, and stability[8].

3. lncRNA and respiratory diseases

In recent years, more and more studies have found that lncRNAs are involved in different respiratory diseases, providing new biomarkers and potential targets for the diagnosis and treatment of respiratory diseases.

In asthmatic patients, the expressions of lnc_00127, lncRNA ANRIL, and lncRNA FTX were up-regulated [10-12], while the expressions of lncRNA CASC7 and lncRNA MEG3 were downregulated. Among them, the expression level of lncRNA MEG3 was the lowest in patients with mixed granulocytic asthma, followed by neutrophils. eosinophilic asthma and eosinophilic asthma, with the highest expression levels in patients with oligogranulocytic asthma[13, 14].

Lin et al.[15] found that lncRNA Hoxaas3 was up-regulated in bleomycin-induced pulmonary interstitial fibrosis and TGFβ1-induced human lung fibroblasts (HPF) fibrosis models.Overexpression of Hoxaas3 can promote fibrosis, and inhibition of Hoxaas3 can inhibit lung fibrosis in vitro and in vivo by regulating miR-450b-5p.

Marina et al. [16] analyzed by next-generation sequencing that the expression of lncRNA IL7AS and MIR3142HG was significantly increased in the HPF inflammation model induced by interleukin-1β (IL-1β). After knockdown of these two lncRNAs, IL7AS was found to negatively regulate IL-6 release, while MIR3142HG was a positive regulator of IL-8 and CCL2 release. Subsequent comparison with idiopathic Pulmonary Fibrosis (IPF) fibroblasts showed no change in the expression of lncRNA IL7AS, while the expression of MIR3142HG and miR-146a was significantly reduced,which was consistent with IL-6, IL-8 associated with a decrease in CCL2 release. Given that lncRNA MIR3142HG knockdown significantly reduced the release of IL-8 and CCL2, and partially reduced the release of IL-6 in IPF fibroblasts, suggesting that the reduced inflammatory response in IPF fibroblasts is associated with attenuated expression of MIR3142HG/miR-146a related.

LncRNAs play crucial roles in the growth, metastasis and invasion of lung cancer cells. Through microarray analysis and transcriptome sequencing, hundreds of lncRNAs have been found to be associated with lung cancer.Ku et al.[17] found that the expression of lncRNA LINC00240 was significantly increased in lung squamous cell carcinoma cells. After knockdown of LINC00240, miR-7-5p was up-regulated in lung cancer cells, resulting in down-regulation of EGFR and inhibited cell invasion and migration ability, suggesting that the LINC00240/miR-7-5p/EGFR axis may play a role in the invasion and invasion of squamous cell carcinoma. important role in migration. Qiang et al. [18] showed that the expression of lncRNA DANCR was elevated in lung cancer, especially in high-grade lung cancer tissues and invasive cancer cells. Overexpression of DANCR can induce lung cancer cell proliferation and colony formation, and interference with DANCR expression can effectively inhibit the progression of lung cancer in vitro and in vivo. Ren et al.[19] found that the expression of HOTAIR was increased in lung adenocarcinoma and lung squamous cell carcinoma, and the expression level was higher than that in adjacent tissues, and there was no significant difference in the expression between male and female patients.

4. lncRNA and COPD

4.1 COPD triggers and lncRNAs

Chronic obstructive pulmonary disease (COPD) is often caused by the interaction of genetic and environmental risk factors.

4.1.1 Environmental factors and lncRNACigarette smoke(CS) and PM 2.5 are the two major environmental risk factors. Long-term exposure to tobacco and PM 2.5 can affect lung function levels, increase COPD morbidity and mortality,shorten life expectancy, and increase the burden on the population.

4.1.1.1 The effect of PM 2.5 on COPD patients and its association with lncRNAs

With the increasing carbon emissions such as automobile exhaust and industrial pollution, the impact of atmospheric fine particulate matter (PM 2.5) on respiratory diseases has gradually been paid more and more attention. Between 2001 and 2014, Bo et al. recruited a total of 133,119 adults (18 years or older) in Taiwan to undergo at least two standard physical examinations, including spirometry tests.PM 2.5 concentrations in Taiwan increased between 2002-2004 and began to decline around 2005. The results showed that with the reduction of PM 2.5, the subjects' mean values of various lung function indicators improved[20].

Li et al.[21] found that PM 2.5-induced human bronchial epithelial cells (Human Bronchial Epithelial Cells, HBEC) lncRNA CCAT1, lncRNA MEG3, lncRNA HOTAIR, lncRNA GAS5 and lncRNA MT1JP expression were significantly up-regulated, which accelerated the apoptosis of cells, and the We demonstrated that lncRNA MEG3 mediates apoptosis and autophagy by increasing the expression of p53 in PM2.5-treated HBE cells, and silencing lncRNA MEG3 inhibited apoptosis and autophagy in HBE cells.

Zhao et al.[22] found that the expression of lncRNA RP11-86H7.1 was significantly up-regulated in human bronchial epithelial cells exposed to environmental stimulation of traffic-related air pollution particulate matter 2.5 (TRAPM 2.5). Mechanistic studies have shown that it may be involved in the inflammatory response induced by TRAPM 2.5 by activating the NF-κB signaling pathway. In addition, lncRNA RP11-86H7.1, as an endogenous competing RNA(ceRNA) of miR-9-5p, could reverse the inhibitory effect of its target gene NFKB1 and maintain the activation of NF-κB, thereby promoting the inflammatory response.

4.1.1.2 Effects of cigarettes on COPD patients and their association with lncRNAs

Smoking can accelerate lung aging and is closely related to the occurrence and development of various lung diseases. Studies by Tran[23] and others showed that exposure of HBEC to cigarette smoke extract (CSE) caused an imbalance of protease balance,resulting in accumulation of ubiquitinated proteins and impairment of the autophagy marker p62 in aggregates, which acted as a trigger for COPD - Potential mechanisms of the pathogenesis of emphysema.

Zhang et al.[24] found that in the COPD mouse model of chronic cigarette smoke extract (CSE), 109 lncRNAs were significantly differentially expressed compared with the control group. Combined with high-throughput data analysis and qRT-PCR validation results,it was suggested that the lncRNA NR_102714 and its related factors in CSE-induced COPD mouse model, cigarette-induced 16HBE cells and peripheral blood mononuclear cells (PBMC) of COPD patients The protein-coding gene UCHL1 plays a role in the pathogenesis of COPD in both mice and humans.

Qin et al.[25] found that CSE could reduce the expression of lncRNA SNHG5 in 16HBE cells. Since SNHG5 acts as a ceRNA of miR-132 in COPD, low expression of SNHG5 increased the expression of miR-132 target protein PTEN. The overexpression of SNHG5 in 16HBE cells attenuated the effects of CSE on cell proliferation, apoptosis and inflammation (IL-1β, IL-6 and TNF-a).Studies by Gu[26] suggested that the expression of LncRNA TUG1 was increased in sputum cells and lung tissue samples of COPD patients, and was negatively correlated with FEV1%, and downregulation of TUG1 reversed CSE-induced airway remodeling.

4.1.2 Genetic factors and lncRNADeficiency of α1-antitrypsin is the only known factor associated with genetic susceptibility to COPD. However, in recent years,studies have reported that there are still other influencing factors related to genetic susceptibility.

In the study on the correlation between CYP2B6 single nucleotide polymorphisms (SNPs) and COPD risk in Hainan population, it was found that the rs4803420 locus in the CYP2B6 gene was associated with reduced COPD risk, while rs1038376 and rs12979270 had adverse effects on COPD risk. Among them, rs4803420 and rs1038376 were significantly associated with both male and female COPD risk, while rs12979270 was only associated with female COPD risk[27].

Zhou et al.[28] found that the rs699467 locus of lnc01414 and the rs7815944 locus of lnc00824 may be protective factors for the occurrence of COPD. rs298207 of lnc01414 is associated with an increased risk of COPD in the entire population, and may have a higher susceptibility to COPD at age ≤70 years. The rs298207 and rs7815944 variants were associated with COPD risk in men.

4.2 The effect of lncRNA on airway and lung tissue cells

A study showed that compared with normal lung tissue, 120 lncRNAs were overexpressed and 43 lncRNAs were underexpressed in COPD patients[29]. The pathological changes of chronic obstructive pulmonary disease exist in the airway, lung parenchyma,and pulmonary blood vessels. In the central airway, it is mainly manifested by inflammatory cell infiltration (eg, macrophages,neutrophils, B cells, T cells), while in the peripheral small airways,airway remodeling, including proliferation and hypertrophy of smooth muscle cells[30-32].

4.2.1 The effect of lncRNA on airway remodeling

Zhao et al.[33] found that the expression of lncRNA MCM3APAS1 in the plasma of COPD patients was down-regulated, and the expression of MCM3AP-AS1 was significantly increased after treatment. Among smokers, patients with low MCM3AP-AS1 expression had a higher incidence of COPD. Cell proliferation experiments showed that overexpression of MCM3AP-AS1 could reduce the proliferation rate of bronchial smooth muscle cells(HBSMCs), while low expression of MCM3AP-AS1 had the opposite effect.

Zheng et al.[34] collected lung tissue from non-smokers, smokers,or smokers with COPD for RNA sequencing. By comparison,it was found that the lncRNA COPDA1 was up-regulated in the lung tissue of COPD patients. Further studies found that COPDA1 overexpression increased MS4A1 gene expression and calcium storage entry in HBSMCs, and thus promoted smooth muscle cell proliferation and airway remodeling. In addition, loss of COPDA1 reduced the expression levels of cell cycle regulatory proteins,namely G1/S-specific cyclin-D1 (cyclin D1) and retinoblastoma protein (pRb). Cyclin D1 and pRb are critical for regulating cell cycle transition and are required for the proliferation of HBSMCs.COPDA1 can promote the proliferation of HBSMCs by regulating cyclinD1 and pRb.

4.2.2 Link between lncRNA and inflammatory cell infiltration

Macrophages are divided into classically activated macrophages(M1) and alternatively activated macrophages (M2)according to their phenotype. Classically activated M1-type macrophages exert pro-inflammatory and cytotoxic effects, whereas M2-type macrophages can promote the secretion of IL-10, exert anti-inflammatory effects, and promote tissue repair and wound healing[35]. Li et al.[36] found that LncRNA MIR155HG was highly expressed in macrophages of COPD patients induced by granulocytemacrophage colony stimulating factor (GM-CSF). Elevation of MIR155HG promotes GM-CSF-induced M1 macrophage polarization and inflammatory cytokine release, whereas decreased MIR-155HG expression increases M2 macrophage polarization,which has the opposite effect.

Qi et al.[37] showed that lncRNAs NR-026690 and ENST00000447867 were up-regulated in CD4+ T cells of patients with acute exacerbation of COPD, and at the same time, The transcript levels of their target genes Rap guanine nucleotide exchange factor 3 (RAPGEF3) were significantly higher than those in stable COPD and healthy people. The transcriptional expression of RAPGEF3 was positively correlated with lncRNAs NR-026690 and ENST00000447867, suggesting that lncRNAs NR-026690 and ENST00000447867 may act as miRNA sponges to affect RAPGEF3 and regulate the development of COPD.

4.2.3 Links between lncRNAs and pulmonary blood vesselsZhou et al.[38] showed that lncRNA HOXA-AS2 was significantly down-regulated in lung tissue of COPD patients and human pulmonary microvascular endothelial cells (HPMECs) which exposed to CSE, and HOXA-AS2 expression in HPMECs exposed to CSE decreased in a dose-and time-dependent manner.LncRNA HOXA-AS2 can promote the proliferation of HPMECs by upregulating its downstream molecule Notch1, and alleviate the damage of CSE exposure to cell viability.

Bi et al.[39] showed that with the increase of CSE exposure, the expression level of lncRNA MEG3 in HPMEC gradually increased,and the B-cell lymphoma-2 (Bcl-2) gene decreased and increased Bcl-2 Associated X Protein (Bax) expression level. Afterwards, the overexpression of lncRNA MEG37 by LncRNA MEG3 plasmid transfection found that the activity of caspase-3 in HPMECs was enhanced and the apoptosis rate was increased, while knockdown of lncRNA MEG3 showed the opposite effect. Further studies showed that lncRNA MEG3-shRNA could significantly reduce the level of lncRNA MEG3 in CSE-induced HPMECs, reversed the effects of CSE on caspase-3 activity and apoptosis-related gene expression,and inhibited cell growth. Apoptosis, protection against CSE-induced HPMECs.

Chen et al.[40] found that the expression of lncRNA TUG1 was increased in CSE-induced HPMEC, while the expression of miR-9a-5p was decreased, promoting apoptosis. CSE-induced apoptosis of HPMECs was reduced by knockdown of lncRNA TUG1, and this effect was reversed by downregulation of miR-9a-5p. The mRNA expression of BCL2L11 was increased in HPMECs after CSE induction, and miR-9a-5p reversed the increase in CSEinduced apoptosis by inhibiting the expression of BCL2L11 in HPMECs, suggesting that BCL2L11 is a direct target gene of miR-9a-5p, suggesting that lncRNA TUG1 plays a role in CSE-induced apoptosis by regulating the miR-9a-5p/BCL2L11 axis.

4.3 The effect of drugs on lncRNA

Dexmedetomidine, an α2-adrenoceptor agonist, is mainly used for sedation during the perioperative period, endotracheal intubation and mechanical ventilation, and has a protective effect on inflammatory lung injury[41]. Du et al.[42] showed that lncRNA PACER was highly expressed in the serum of COPD patients.Subsequently, by establishing a COPD rat model, it was found that overexpressed PACER in rat alveolar epithelial cells enhanced cell proliferation and migration by activating protein phosphatase 2.After dexmedetomidine treatment, it reduced the PACER expression,proliferation and migration ability of alveolar epithelial cells in COPD rats, which was helpful for COPD treatment.

Andrographolide is a common anti-inflammatory drug, which can reduce the expression of inflammatory cytokines caused by cigarette smoke and infection. Xia et al.[43] found that in human bronchial epithelial cells exposed to CSE, inflammatory factors such as IL-6 and IL-8 increased, which activated downstream signal converter and activator of transcription 3 (STAT3), thereby up-regulating lncRNA HOTAIR and IL-8. Expression of zeste homolog enhancer 2 (EZH2). Andrographolide reversed CSE-induced HB inflammation and epithelial-mesenchymal transition by reducing IL-6 levels, and in animal models, it prevented CSE-induced lung inflammation and small airway remodeling, suggesting that andrographolide It has potential clinical application value for cigarette-induced pulmonary dysfunction and COPD.

5. Prospect

With the development of high-throughput sequencing, people's understanding of lncRNA is gradually deepening. From the "noise"of genome transcription at the beginning, to the involvement of cell growth, differentiation, reproduction, and the pathological outcome of diseases, lncRNAs have great potential to become biomarkers.

From 1990 to 2017, chronic obstructive pulmonary disease has been the fourth leading cause of death in my country[44]. Therefore,research on its diagnosis, treatment and prognosis cannot be stopped.Numerous studies have shown that a variety of lncRNAs play important roles in various stages of COPD budding, development,transformation, and outcome, making them attractive targets for therapeutic intervention. However, the underlying molecular mechanisms of lncRNAs in COPD are still to be completed, and there are few studies on the effects of COPD therapeutic drugs on lncRNAs, and continuous efforts are still needed in the future to achieve early diagnosis, early treatment, and improvement of prognosis evaluation. Quality of life of patients and reduce social burden.

Author's Contribution Statement He Chanyi: topic selection, thesis structure design, literature collection, writing, and revision; Ding Yipeng: mainly reviewing the topic selection and the intellectual content of the article.

Conflicts of Interest All authors declare that this article has no conflicts of interest.